Carrier frequency telephone system



June 29,- 1943. w. HAGEN' 2,323,033

CARRIER FREQUENCY TELEPHONE SYSTEM Filed A ril 22, 1941 M2 I o 326, E ,6 i

I I 'J iNvENToR War-anus Haas/v A'ITORNEY I Patented June 29, 1943.

UNITED STATES. PATENT F FlCE caanmn FREQUENQY TELEPHONE srs rEM Wolfgang Hagen, Berlin, Germany; vested in-the Alien Property Custodian Application April 22, 1941, Serial No. 389,714

In Germany March 13, 1940 9 Claims. '(Cl. ire-4 The present invention relates to carrier ,fre-' quency telephone systems, and more particularly to systems of the lgind in which a pair of conductors forms the transmission channels necessary in establishing two-way intercommunication.

The heretofore known two-way-carrier frequency communication systems, in which a single pair of conductors forms the transmission line, generally employ. different frequency ranges for each direction of transmission. This facility, however, introduces the disadvantages that in the first instance the one transmission channel offers an attenuation which is different from thatof the other. channel and, on the other hand, that the frequency band subject to transmission over the line is at least twice as wide as that of the normal voice frequency band. Apart from these inconveniences, separate filter means must be provided in order to segregate these different frequencies.

It is the primary object of this invention to provide a twoeway carrier frequency telephone system in which the same frequency band may be employed in both directions of communication, and it is a further object of the invention to ensure stability of such a system.

In obtaining the objects stated above, the normal voice frequencies emitted in both directions of communication are so transposed within the same band that the corresponding transmission band frequencies are reversed, that is, the transposition frequency employed inone direction is located at the lower end and the transposition frequency in the opposite direction is located ,at

the upper end of the transmission frequency band. In order to impress these frequencies upon and derive them from the common transmission line, the terminal or intermediate stations may suitably be provided with line branches which either include the requisite number of filter means or form a suitable combination therewith. The fact that the same voice frequency determines the mean frequency of the wave-band in .both operating directions may cause an instable condition at this mean frequency, but this injunction with the accompanying drawing, in which Y Fig. 1 shows one embodiment of a two-way. I

carrier frequency communication system according to the invention, while Fig. 2 shows its application to a two-wire line amplifier.

The system exemplified in Figic-perates in the following manner. Voice frequency oscillations, say between 300 and 2700 cycles, incoming over the line NFI are selected by the line branch G1 andapplied to amodulator M1 through a filter F1 which excludes the mean frequency of 1500 cycles. The remaining frequencies of the voice frequency band are then transposed in the modulator M1 into an intermediate frequency band of the same width including the frequency range between 3300 and 5700 cycles in such manner, that the intermediate frequency of 3300 v cycles is obtained from the 300 cycles voice freconvenience can be eliminated by so designing the filters that the mean frequency is excluded,

that is, not employed for the voice frequency transmission. This facility involves the further advantage that the said mean frequency of the band may be'used as ringing frequency which thus remains unaffected by speec e The invention will be clearly understood from the following detailed description taken in confrequency band to a demodulator D2 which transposes the above-mentioned intermediate frequency band back into the original voice frequency range, that is, into the band-covering the frequencies between 3.00 and 2700 cycles. An

incoming intermediate frequency of 4500 cycles is converted into 1500 cycles, which frequency actuates a ringing current responsive device R: in the output circuit of the demodulator D2 which device in turn applies ringing current to the outgoing line NFz.

/ Whena line branch, such as G1, is used, a balancing network Ni must be combined therewith in order to balance the line L with respect to the intermediate frequency band between 3300 and 5700 cycles. Such balancing will be readily obtained since this transmission band is rather narrow. a

In the op ite direction of communication, that is, from line NF: to line NFI, the same voice frequency band between 300 and 2700 cycles is used. The modulator M2v effects transposition thereof into an intermediate frequency band ranging between 3300 and 5700 cycles which band nected to this line.

is transmitted over the line L and impressed upon a demodulator D1 which transposes this hand back into the voice frequency band between 300 and 2700 cycles. In this direction of operation, however, the 300 cycles voice freque is converted into an intermediate frequen of 5700 cycles, while the 2700 cycles voice frequency is converted into an intermediate frequency of 3300 cycles by means of a modulation or transposition frequency of 6000 cycles. The fact that the frequency characteristic used in onedirection opposes that of the other direction, eliminates each singing tendency even in the presence of balancing faults. Let it be assumed that the 300 cycles frequency is incoming over the line NF; and applied to the modulator Ml. There will then appear a frequency of 3300 cycles in the output circuit of this modulator and a part of 'this frequency will due to the balancing fault in the network N1 obtain access to the demodulator D1 which in turn transposes this frequency into 2700 cycles. This last-mentioned frequency is then applied to the line NFl and will, be heard as an unintelligible noise in the telephone con- It will further be assumed that a balancing fault is also introduced at the network N1, in which case this frequency of 2700 cycles would be converted into a frequency of 5700 cycles in modulator M1 and then into a frequency of 300 cycles in the demodulator Di. It is thus clear that the distance from the singin point for one terminal station is twice as large as the attenuation of the loop circuit at this station, that is, the attenuation of the path Mi, G1, D1, G1, M1.

The Fig. 2 shows the invention as applied to a two-wire line amplifier. Communication from line NF! to line NF: is effected through line branch G1, voice frequency amplifier A1, line branch G1, over the line L, and through the line branch G1, voice frequency amplifier A2, and line branch G1 to the line NFa. In the opposite direction of operation, the voice frequencies are subjected to a reversal in the modulator M2, that is, the frequency of 300 cycles is converted into a frequency of 2700 cycles and the voice frequency of 2700 cycles is converted into a frequency of 300 cycles, which is readily possible by subjecting the voice frequency band between 300 and 2700 cycles to a first modulation with 8000 cycles. The resulting lower side-band including the frequencies of 5300 to 7700 cycles is then again modulated with a modulation frequency of 5000 cycles resulting in a voice frequency band of 300 to 2700 cycles. The frequency characteristic of this band is opposite to that of the voice frequencies. The 1500 cycles mean frequency of this band must be particularly considered with respect to the balancing of the line since the singing tendency becomes more severe at this frequency. However, in contradiction to the usual low frequency twowire line amplifiers, in which a uniform and sattransmission in both directions of operation comprising, a two-wire transmission line interconnecting said stations, means in said stations for producing a voice frequency band, means in one of said stations for transposing said voice frequency band intosaid transmission band by the use of a modulating frequency adjacent the lower end of said transmission band, and means in the other of said stations for transposing said voice frequency band into the same transmission band by the use of a modulating frequency adjacentth upper end of said transmission band.

2. A two-wire carrier frequency telephone systern for effecting two-way communication between terminal stations by utilizing the same transmission band in the frequency spectrum for transmission in both directions of operation comprising, a two-wire transmission line interconnecting said stations, means in said stations for producing a voice frequency band, means in one of said stations for transposing saidvoice frequency band into said transmission band by the use of a modulating frequency adjacent the lower end of said transmission band and for selecting the upper side-band of the transposition product for transmission over said line, and means in the other of said stations for transposing said'voice frequency bandinto the same transmission band by the use of a modulating frequency adjacent the higher end of said transmission band and for selecting the lower side-band of the transposition product for transmission over said line for inverting the frequency characteristic of said last-mentioned transmission band with respect to the frequency characteristic of said voice frequency band.

3. A two-wire carrier frequency telephone system according to claim 2, wherein the said voice frequency band is subjected to at least two different frequency transpositions.

4. A two-wire carrier frequency telephone system according to claim 2, wherein line branches are provided for interconnecting said terminal stations with said transmission line.

5. A two-wire carrier frequency telephone system according to claim 2, wherein balancing networks are provided in the terminal stations for balancing said line with special reference to. the

i mean frequency of the said transmission band and the said voice frequency band, respectively.

6. A two-wire carrier frequency telephone system according to claim 2, wherein the distance from the singing point for one terminal station is twice as large as the attenuation of the loop circuit at said station.

7. A two-wire carrier frequency telephone system according to claim 2, wherein means are provided for suppressing the mean frequency of the said voice frequency band and the said transmission band, respectively.

8. A two-way electric wave signalling system comprising a first terminal station, a second terminal station, a two-wire transmission line extending between said first and said second stations, means in said stations for producing voice frequency signal waves, means in one of said stations for impressing upon said transmission line waves containing voice frequency signal components and extending over a predetermined frequency band in which the frequency amplitude characteristic of the voice frequency signal waves is inverted and means in the other station for impressing upon said transmission line waves containing voice frequency signal components and extending over the same predetermined frequency band but in which the frequency amplitude characteristic of the voice frequency signal waves is unchanged.

9. A two-way electric wave signalling system comprising a first repeater station, a second repeater station, a two-wire on line ex-- tending between said tirstand second stations, means in said stations for producing voice frequency signal waves extending over a predetermined band in the frequency spectrum, means 1 in. one'ot said stations for impressing upon said transmission line waves extending over said pre- WOLFGANG HAGEN. 

